The present invention relates to a method of decreasing nitrate nitrogen and volatile organic compounds present in soil and groundwater.
Recently, there is found explicit pollution by nitrate nitrogen in soil and groundwater caused by high density agriculture and excess fertilizing for cultivating crops requiring high nitrogen fertilization typified by tea cultivation.
As the countermeasure for such pollution of groundwater, there is already known a technology of evacuating groundwater to ground and concentrating and removing nitrate nitrogen using an ion exchange resin. As the example of such technology, there is one described in “Yosui to Haisui (irrigation water and waste water)” published by Sangyo Yosui Chosakai, vol. 34, No. 7 (1992), Yusaku Miyake, “Ionkokanjushi niyoru Chikasuichu no Shosanseichisso jokyo (removal of nitrate nitrogen in groundwater by ion exchange resin)”.
As the method of removing nitrate nitrogen in soil, there is a biological denitrification method. As the example using this biological denitrification method, there are well known examples such as an example using soy bean oil as a carbon source for a denitrification bacteria (“Yosui to Haisui (irrigation water and waste water)” published by Sangyo Yosui Chosakai, vol. 41, No. 10 (1999), Daichi Maruoka, “Shosansei.Ashosansei Chisso Osen Chikasui no Bioremediation (bioremediation of nitrate.nitrite nitrogen-polluted groundwater)” an example of adding high test syrup and/or isomerized sugar to soil (Japanese Laid-open Patent Application No. Hei 6-169641), an example of adding a carrier for a denitrification bacteria to soil (Japanese Laid-open Patent Application No. Hei 11-128902), an example of adding a fermentation material obtained by using seaweeds and diatomaceous earth to soil (Japanese Laid-open Patent Application No. 2001-8550) and the like.
Further, regarding volatile organic compounds such as dichloromethane, carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene, tetrachloroethylene, benzene, 1,3-dichloropropene and the like in soil and groundwater, there is a problem of secondary pollution by discharge of these volatile organic compounds into environment. As the method of decreasing a volatile organic compound to prevent such secondary pollution, there is a method which utilizes microorganisms present in soil. It is known that such microorganisms are effectively decomposed in the presence of a hydrogen donor and a nutrient salt of phosphorus, nitrogen and the like. A method of decreasing such volatile organic compound is described, for example, in D. E. Ellis, et al., Environmental Science and Technology, 34(11), p2254 (2000). Japanese Laid-open Patent Applications No. Hei 9-276894 and No. Hei 11-90484 disclose methods of decreasing a volatile organic compound using an organic substance which is liquid at normal temperature such as citric acid and ethanol as the hydrogen donor.
The conventional methods of decreasing nitrate nitrogen and volatile organic compounds had the following problems.
In the conventional technology of removing nitrate nitrogen in groundwater, groundwater is once evacuated to the ground and nitrate nitrogen is concentrated by ion exchange, and there was a necessary for reprocessing of the concentrated nitrate nitrogen. Since groundwater is thus once evacuated to ground and subjected to ion exchange treatment, this is not accepted as on site treatment in strict meaning, and there was a problem that the structure is large and complicated.
In the conventional biological denitrification method, since water-soluble organic matter such as saccharides and the like and organic matter which are liquid at normal temperature even if not water soluble are added to soil and groundwater, there was a problem that organic matter move easily and are diffused in soil, and there was a high possibility of occurrence of secondary pollution by organic matter.
Further, regarding the conventional biological denitrification method, in method disclosed in Japanese Laid-open Patent Application No. Hei 11-128902 of adding a carrier for a denitrification bacteria into soil, there was a problem that when an organic substance which can be efficiently utilized by a denitrification bacteria does not co-exist, biological denitrification cannot be effected efficiently and a substance of a denitrification bacteria such as cellulose and the like cannot necessarily become an effective hydrogen donor.
For example, as disclosed in Japanese Laid-open Patent Application No. Hei 2001-8550 the method of using a waste of a certain kind of natural resource as a carbon source is preferable in the aspect of effective utilization of waste, however, since a natural water necessarily contains nitrogen originally, there is contrarily a possibility that such natural waste functions as a nitrogen supply source even in the case of use of such waste for the purpose of removal of nitrogen.
On the other hand, in the case of removal of a volatile organic substance, when a bacteria was used, a hydrogen donor and a nutrient salt of nitrogen, phosphorus and the like were water-soluble, consequently, these were easily diffused in soil and groundwater, leading to a possibility of secondary pollution.